1. Field of the Invention
The present invention relates generally to remote control apparatus, and is directed more particularly to remote control apparatus in which both the likelihood of errors caused by noise and the power required for transmission are reduced.
2. Description of the Prior Art
Remote control apparatus is well known in the prior art. For example, U.S. Pat. No. 3,678,392 discloses a pulse width modulation (PWM) remote control system in which the duration of pulse signals are varied in accordance with the particular command which is to be communicated. It is also disclosed, for example, in U.S. application Ser. No. 846,445 filed on Oct. 28, 1977 that not only the duration of the pulse (T.sub.m in FIG. 1), but also the duration of time between pulses (T.sub.n in FIG. 1) can be varied in accordance with the particular command to be communicated.
In these prior art remote control systems, an ultrasonic, infra-red or similar carrier signal is continuously transmitted for the duration (T.sub.m) of each pulse. This continuous transmission increases the energy required to transmit a command and it increases the likelihood that receipt of the carrier signal will be interrupted by an interferring signal capable of causing the command to be misread.